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Venus at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

Objects: Venus
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The sky at

Venus will reach half phase in its 2018 evening apparition. It will be shining brightly at mag -4.3.

From Cambridge , this apparition will not be one of the most prominent but prominent, reaching a peak altitude of 27° above the horizon at sunset on 7 Jun 2018.

Begin typing the name of a town near to you, and then select the town from the list of options which appear below.

The table below lists how high Venus will appear at sunset over the course of the apparition. All times are given in Cambridge local time.

Date Sun
sets at
sets at
at sunset
at sunset
09 Mar 201817:4318:5313°west
19 Mar 201818:5520:1715°west
29 Mar 201819:0620:4218°west
08 Apr 201819:1721:0820°west
18 Apr 201819:2921:3322°west
28 Apr 201819:4021:5824°west
08 May 201819:5122:2025°west
18 May 201820:0122:3926°west
28 May 201820:1122:5127°west
07 Jun 201820:1822:5727°west
17 Jun 201820:2322:5626°west
27 Jun 201820:2522:4925°west
07 Jul 201820:2322:3824°west
17 Jul 201820:1722:2222°west
27 Jul 201820:0922:0421°west
06 Aug 201819:5721:4419°west
16 Aug 201819:4421:2217°south-west
26 Aug 201819:2820:5815°south-west

A graph of the phase of Venus is available here.

Observing Venus

The 2018 evening apparition of Venus
07 Jun 2018 – Venus reaches highest point in evening sky
15 Aug 2018 – Venus at dichotomy
17 Aug 2018 – Venus at greatest elongation east
25 Sep 2018 – Venus at greatest brightness

Venus's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is lost in the Sun's glare much of the time.

It is observable for a few months each time it reaches greatest separation from the Sun – moments referred to as greatest elongation. These apparitions repeat roughly once every 1.6 years.

On these occasions, Venus is so bright and conspicuous that it becomes the third brightest object in the sky after the Sun and Moon. It is often called the morning star or the evening star.

Venus's phase

Venus's phase varies depending on its position relative to the Earth. When it passes between the Earth and Sun, for example, the side that is turned towards the Earth is entirely unilluminated, like a new moon.

Conversely, when it lies opposite to the Earth in its orbit, passing almost behind the Sun, it appears fully illuminated, like a full moon. However, at this time it is also at its most distant from the Earth, so it is actually fainter than at other times.

Venus shows an intermediate half phase – called dichotomy – at roughly the same moment that it appears furthest from the Sun, at greatest elongation. The exact times of the two events may differ by a few hours, only because Venus's orbit is not quite perfectly aligned with the ecliptic.

Venus's position

The coordinates of Venus when it reaches dichotomy will be:

Object Right Ascension Declination Constellation Angular Size
Venus 12h27m10s -04°20' Virgo 23.7"
Sun 09h37m +14°08' Leo 31'34"

The coordinates above are given in J2000.0.

The sky on 15 August 2018
Twilight ends
Twilight begins

4-day old moon
Waxing Crescent


4 days old

Rise Culm. Set
Mercury 05:08 12:03 18:57
Venus 09:52 15:38 21:24
Moon 10:50 16:40 22:30
Mars 19:03 23:19 03:39
Jupiter 12:54 17:59 23:04
Saturn 16:45 21:19 01:57
All times shown in EDT.


The circumstances of this event were computed using the DE405 planetary ephemeris published by the Jet Propulsion Laboratory (JPL).

This event was automatically generated by searching the ephemeris for planetary alignments which are of interest to amateur astronomers, and the text above was generated based on an estimate of your location.

Related news

15 Aug 2018  –  Venus at dichotomy
17 Aug 2018  –  Venus at greatest elongation east
05 Sep 2018  –  Venus at aphelion
25 Sep 2018  –  Venus at greatest brightness

Image credit

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